ENH: added an optional argument to the constructor of patchWave

This provides a list of faces (can be internal ones) to act as
additional seeds for the wave algorithm. The default argument provides
an empty list, so the behaviour of patchWave should not change.

Useful in topology optimisation, for propagating the active design
variables from the seed faces to the interior, with a given number of
cells at a time.

src/meshTools/cellDist/patchWave/patchWave.C

@@ -66,6 +66,20 @@ void Foam::patchWave::setChangedFaces
             }
         }
     }
+
+    for (const label facei : sourceIDs_)
+    {
+        changedFaces[nChangedFaces] = facei;
+
+        faceDist[nChangedFaces] =
+            wallPoint
+            (
+                mesh.faceCentres()[facei],
+                0.0
+            );
+
+        nChangedFaces++;
+    }
 }
 
 
@@ -137,7 +151,8 @@ Foam::patchWave::patchWave
 (
     const polyMesh& mesh,
     const labelHashSet& patchIDs,
-    const bool correctWalls
+    const bool correctWalls,
+    const labelList& sourceIDs
 )
 :
     cellDistFuncs(mesh),
@@ -145,7 +160,8 @@ Foam::patchWave::patchWave
     correctWalls_(correctWalls),
     nUnset_(0),
     distance_(mesh.nCells()),
-    patchDistance_(mesh.boundaryMesh().size())
+    patchDistance_(mesh.boundaryMesh().size()),
+    sourceIDs_(sourceIDs)
 {
     patchWave::correct();
 }
@@ -163,7 +179,7 @@ void Foam::patchWave::correct()
 {
     // Set initial changed faces: set wallPoint for wall faces to wall centre
 
-    label nPatch = sumPatchSize(patchIDs_);
+    label nPatch = sumPatchSize(patchIDs_) + sourceIDs_.size();
 
     List<wallPoint> faceDist(nPatch);
     labelList changedFaces(nPatch);